The present invention relates to a method of energy conversion of solid fuels containing carbon.
The emission of greenhouse gases, in particular CO2, in power stations using fossil fuels must increasingly be brought under control. Controlling such emission entails solving new problems such as capturing the CO2 in the flue gases of power stations using fossil fuels or in the gases from installations using biomass type renewable energy sources (non-fossil carbon) for the production of substitute fuels usable in transportation, and all of the above combined while minimizing the cost and minimizing the modification of existing installations.
Finally, the progressive depletion of oil fields is generating a dynamic for the large scale deployment of recovery techniques assisted by injecting CO2 that are capable of doubling the extraction capacities of accessible reserves.
To this end, it is known in the art to use oxygen and steam to convert solid fuels containing carbonaceous materials by autothermic gasification to produce a syngas containing CO and H2 that may be used in gas turbines, hydrogen production units or units for synthesizing methanol type compounds.
The above type of installation is described in our patents FR 2 660 415 and FR 2 559 776. However, the presence of unconverted tar or fine unburned carbon particle type hydrocarbons in these installations creates unwanted condensation and unwanted components in the cooling and syngas processing systems and degrades the yield from such installations.
To eliminate the tar and unburned carbon, the syngas is subject to a thermal reforming process by increasing the temperature resulting from partial combustion, which necessitates an additional supply of secondary oxygen.
As described in our U.S. Pat. No. 6,505,567, it is also possible to convert these solid fuels energetically by employing combustion processes using oxygen and recycled CO2, rather than external air, which produces combustion flue gases containing principally CO2 and steam, with no nitrogen, in order to be able to use these flue gases for operations of assisted recovery of subterranean petroleum or to enable their subterranean storage. However, these processes consume a great deal of oxygen, which must be produced by a dedicated air distillation unit using some of the energy produced, and therefore adding to the electrical energy consumption burden.
Also known in the art is using thermochemical cycles in combustion processes for converting solid fuels containing carbonaceous materials to produce combustion flue gases containing principally CO2 and water. With this solution, it is not necessary to use a dedicated air distillation unit, but a problem arises from the presence in the combustion flue gases of unconverted carbonaceous compounds, such as hydrocarbons (CnHn) or unburned carbon, which are unacceptable for assisted petroleum recovery processes or subterranean storage and must be eliminated.
The object of the present invention is to propose an energy conversion method that minimizes the consumption of oxygen and minimizes the production of unconverted carbonaceous compounds.